1. Field of the Invention
The present invention relates to pulse generators and more particularly to pulse generators having a predetermined frequency and duty cycle, such as are capable of integrated circuit fabrication. The invention further relates to low current circuitry employing complementary metal oxide semiconductor (CMOS) field effect transistor technology.
2. Description of the Prior Art
The need has arisen for a pulse generator formed 10 on an integrated circuit having a low current drain, a controllable frequency and a selected duty cycle. The frequency should be controllable externally to the integrated circuit with a minimum component count and a minimum pad count. The application also requires that the frequency and duty cycle have a high degree of temperature stability.
In the practical application envisioned for the invention, the desired center frequency is 100 Khz with an at least 3 to 1 range of possible adjustment (60-180 Khz). The desired duty cycle is near 20% temperature stability of frequency and duty cycle over a wide temperature range (typically 20.degree.-125.degree. C.) is also sought.
It is known that a ring oscillator can be readily fabricated using CMOS technology. In the known example, the oscillator is not a part of the working circuit, but is used to test the process by which the working circuit is formed on the integrated circuit. Typically it includes as many as 19 stages, since the power and chip area requirements are small. The present invention makes an adaptation of the ring oscillator approach in the provision of a pulse generator having the desired performance characteristics.